Background Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) are a group of autoimmune disorders that result in systemic inflammation with distinct clinical manifestations. These further categorize this pathology into three unique subtypes. First, Granulomatosis with Polyangiitis (GPA) (previously Wegener's Granulomatosis) is associated with the PR3–ANCA autoantibody and is known for its inflammatory destruction of upper and lower respiratory tracts, as well as renal small vessels. Second, Microscopic Polyangiitis (MPA) is another type of AAV that may present similarly to GPA; however, distinct features that separate this subtype include the absence of upper respiratory involvement and the MPO–ANCA antibody predominance. Finally, Eosinophilic Granulomatosis with Polyangiitis (EGPA) (previously Churg-Strauss syndrome) is also associated with MPO-ANCA. However, this rare type of AAV presents with asthma and eosinophilia.  The pathogenesis of all three types of AAVs includes destructive inflammation that begins intravascularly and progresses to tissue destruction and end-organ damage. Early management strategies typically involve glucocorticosteroids, and rituximab and cyclophosphamide are frequently included in patients with severe disease. 

Case Presentation Here, we present a clinical case of MPO–ANCA positive vasculitis with a benign presentation of epigastric pain and poor appetite that rapidly progresses into systemic inflammation with pulmonary and renal manifestations. In this case, an 81-year-old female with no known medical history presents with mild chronic epigastric pain and poor appetite. Clinically, the patient was stable and well-appearing, with no apparent signs of deterioration at the bedside. Early laboratory investigations were consistent with mild anemia and chronic kidney disease. Lung imaging demonstrated diffuse airspace opacities and tree-in-bud pulmonary nodules.  Screening for infectious etiologies, including bacterial (including tuberculosis), viral, and fungal, were negative. As inflammatory markers continued to uptrend, secondary inflammatory etiologies were explored, resulting in the discovery of a positive MPO–ANCA autoantibody test.  This was followed by rapid deterioration into acute hypoxemic respiratory failure, requiring mechanical ventilation, and complicated by diffuse alveolar hemorrhage, in addition to severe anemia requiring multiple transfusions and acute kidney failure.

Discussion This clinical case highlights the rapidly progressing nature of AAVs and the frequent benign presentations that can masquerade as this aggressive pathology. As the literature continues to evolve and offer recommendations on the management of these rare autoimmune diseases, early recognition, diagnosis, and intervention are essential to minimize mortality and morbidity rates and offer patients a relapse-free prognosis and improved clinical outcomes.